Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $250.66   6.832%   $267.7851   $267.79   $267.80   $267.80  
  Purchase #2 $142.38   6.774%   $152.0248   $152.02   $152.00   $152.00  
  Purchase #3 $200.92   8.785%   $218.5708   $218.57   $218.55   $218.60  
  Purchase #4 $143.61   9.418%   $157.1352   $157.14   $157.15   $157.10  
  Purchase #5 $61.43   4.679%   $64.3043   $64.30   $64.30   $64.30  
  Purchase #6 $102.73   5.424%   $108.3021   $108.30   $108.30   $108.30  
  Purchase #7 $44.91   5.315%   $47.297   $47.30   $47.30   $47.30  
  7 purchase totals = $946.64       $1,015.4193   $1,015.42   $1,015.40   $1,015.40